The present invention relates to a molding die, a sol-gel composition produced using the die, and a process for producing a sol-gel composition. More particularly, the invention relates to a molding die applicable to the production of various optical parts such as read-only optical information recording media (CD-ROM), flat microlenses and grating elements, a sol-gel composition produced using the die and a process for producing the sol-gel composition.
A sol-gel method is used to produce various optical parts such as read-only optical information recording media (CD-ROM), flat microlenses and grating elements. This method comprises applying a sol-gel material in a given thickness to a given substrate, pressing a molding die having a given surface shape against the sol-gel material for a given period of time with heating, subsequently separating the molding die from the sol-gel material, and then sintering the sol-gel material to evaporate a solvent, thereby obtaining a sol-gel composition having a desired surface shape and a desired thickness.
In order for the sol-gel method to obtain a sol-gel composition at a higher rate while attaining a reduced rejection rate and improved dimensional accuracy of the sol-gel composition, it is essential to use a molding die having satisfactory releasability from the sol-gel material.
Because of this, the molding dies for use in the sol-gel method have hitherto been made of a suitable resin so as to obtain satisfactory releasability from sol-gel materials.
However, a molding die having even better releasability is desired because the sol-gel method has recently come to be required to attain a higher rate of production, a lower rejection rate, and better dimensional accuracy than conventional ones.
The present invention has been achieved in order to satisfy the demand.
Accordingly, one object of the invention is to provide a molding die having satisfactory releasability.
Another object of the invention is to provide a sol-gel composition produced using the molding die.
Still another object of the present invention is to provide a process for producing the sol-gel composition.
In order to accomplish these objects, the present invention provides a molding die to be pressed against a sol-gel material for producing a sol-gel composition, the molding die having a release film formed on the molding surface thereof to be brought into contact with the sol-gel material.
The release film may be made of any material as long as it has desired properties including: satisfactory releasability from the sol-gel material; a given strength which enables the release film to withstand the pressing pressure applied to the sol-gel material; heat resistance which enables the release film to withstand the heat applied to the sol-gel material; corrosion resistance which enables the release film not to corrode even upon repeated contact with the sol-gel material; and moldability which enables the material to be easily molded into a desired shape. Examples of the material include gold (Au), platinum (Pt), copper (Cu), palladium (Pd), silver (Ag), nickel (Ni), and alloys of two or more thereof.
Since the molding die has such a release film on the molding surface thereof, it shows satisfactory releasability from the sol-gel material in producing a sol-gel composition. As a result, a higher production rate, a lower rejection rate and better dimensional accuracy than conventional ones can be attained.
In a preferred embodiment of the invention, the release film is made of a material comprising one member selected from the group consisting of gold (Au), platinum (Pt), copper (Cu), palladium (Pd), silver (Ag), nickel (Ni) and alloys of two or more thereof.
These materials may be used alone or in combination of two or more thereof as the release film as long as the desired effects are obtained. The release film is not particularly limited in thickness, molding method, etc. The alloys usable as the material of the release film each need not made of all those metals and may be made of two or more of the metals. Where the release film is made of an alloy, the constituent metals may be in any desired proportion.
Since the molding die according to this preferred embodiment has a release film made of a material comprising one member selected from the group consisting of gold (Au), platinum (Pt), copper (Cu), palladium (Pd), silver (Ag), nickel (Ni) and alloys of two or more thereof, the molding surface is unsusceptible to oxidation and is less apt to suffer a change with the lapse of time. As a result, excellent durability is obtained.
In another preferred embodiment of the invention, the die has a substrate for the release film, and the substrate is made of a material comprising one member selected from the group consisting of resins, glasses, metals, and a combination of two or more thereof bonded to each other.
The substrate used may be a suitable material which has the same performances as the release film and has a coefficient of thermal expansion close to that of the release film.
In the molding die according to the preferred embodiment described above, the release film can have a reduced thickness irrespective of the area of the molding surface. Where the substrate is made of a resin, this molding die has an advantage that the substrate material can be finely processed easily and has satisfactory moldability. On the other hand, where the substrate is made of a glass or metal, the substrate has high heat resistance, high strength and excellent durability.
In a further preferred embodiment of the invention, the molding die has a buffer layer made of one or more metals and/or one or more inorganic oxides between the substrate and the release film.
Since the molding die according to the embodiment described above has a buffer layer made of, e.g., aluminum (Al) chromium (Cr) or a tin-doped indium oxide (ITO), between the release film and the substrate, the release film is tenaciously deposited on the substrate through the buffer layer. Namely, compared to molding dies having a release film directly deposited on a substrate, this molding die is less apt to have the possibility that the release film may peel off the substrate, i.e., may be transferred to a sol-gel material. As a result, the molding die can have improved durability.
In still a further preferred embodiment of the invention, the surface of the release film has recesses. These recesses conform with the surface shape of the substrate.
Examples of the shape of each recess include a sphere, cones, pyramids and grooves having any desired cross-sectional shape. Spherical, conical or pyramidal recesses may be formed in a desired number in part or all of the release film surface. Where many such recesses are formed, there are no particular limitations on the relative position thereof. On the other hand, where grooves are formed as recesses, the grooves may be linear or curved and may be formed in a desired number. When grooves are formed, they may be arranged concentrically or in a lattice pattern.
Since the molding die according to the embodiment described above has recesses formed in the surface of the release film, it is possible to produce various optical parts, e.g., read-only optical information recording media (CD-ROM), planar microlenses and grating elements, which have high dimensional accuracy.
The invention further provides a sol-gel composition molded by pressing any of the molding dies according to the invention described above against a sol-gel material.
Since this sol-gel composition is molded with the molding die having a release film formed on the molding surface, a higher production rate, a lower rejection rate and better dimensional accuracy than conventional ones can be attained.
The invention still further provides a process for producing a sol-gel composition which comprises using the sol-gel composition described above as a molding die to be pressed against a sol-gel material.
Since the sol-gel composition thus molded has higher dimensional accuracy than conventional ones, a high precision replica can be obtained.
In a preferred embodiment of the process for producing a sol-gel composition of the invention, the sol-gel composition used as a molding die has functional groups which are releasable from the sol-gel material.
Examples of the functional groups include relatively lowly reactive groups such as methyl, ethyl, isopropyl, 3,3,3-trifluoropropyl and phenyl groups.
According to the preferred embodiment of the process for producing a sol-gel composition, the sol-gel composition for use as a molding die has satisfactory releasability from the release film because the functional groups form an outer layer of the sol-gel composition upon contact with the release film. Consequently, the sol-gel composition can be used as a die for molding a sol-gel material without essentially necessitating a release film made of, e.g., platinum (Pt) or gold (Au).